Okay I'm taking this account briefly out of retirement because Croll's answer is wrong and massively misleading.
Yes, they can (most likely) figure out that it was you, technologically at least.
So the scenario is that you sent an email from some mail server to a group that only you and your classmates know about. Straight away you've acted within a small subset of possible candidates.
From either the mail headers or a subpoena, they can discover that the email was sent over Tor.
From either the mail headers or a subpoena, they can discover when the email was sent.
From the small set of possible candidates, how many of them were connecting to Tor at the time the email was sent? I'm guessing the answer is ~1 (you).
There is precedent for this in the case of the Harvard "Bomb Threat" Hoax who, in 2013, made exactly the same mistake that you have.
The issue is that you created a very small anonymity set, you take a few sets of people: The people who know your friend, the people who know the recipient email address, the people online at the time the email was sent, the people on Tor at the time the email was sent. Now take all these sets and put them on a Venn Diagram. Where all these sets overlap is a very small area, probably consisting of just you.
Now, here's where you might not get caught. Local police departments aren't technologically sophisticated and they don't have a lot of time to devote to it. They'd likely need some kind of warrant or subpoena for all the users internet connection records, I'm not a lawyer so I don't know how plausible that would be in your jurisdiction. If you are already of particular interest to the investigation such that they can show probable cause or reasonable suspicion, then you're going to be getting asked some questions by law enforcement.
Note: It may be noteworthy that the Harvard Student confessed when the FBI questioned him, we didn't get to see this play out in court, so how well he might have been able to maintain plausible-deniability was not tested. But in general what you are doing is not safe or anonymous and there's no technical reason you wouldn't be caught.